Lens system for photoelectrophoretic copying machine

ABSTRACT

A SYMMETRICAL COPYING LENS SYSTEM HAVING FRONT AND BACK COMPOUND LENS COMPONENTS WITH A CENTRALLY LOCATED DIAPHRAGM THEREBETWEEN ADAPTED TO AN OPTICAL SYSTEM OF A PHOTOELECTROPHORETIC COPY MACHINE WHICH CAN BE USED AT 1:1 MAGNIFICATION. THE FRONT LENS COMPONENT HAS FOUR LENS ELEMENTS INCLUDING IN THE FOLLOWING ORDER , A FIRST LENS ELEMENT OF POSITIVE POWER, A SECOND LENS ELEMENT OF POSITIVE POWER, A THIRD LENS ELEMENT OF POSITIVE POWER AND A FOURTH LENS ELEMENT OF NEGATIVE POWER CEMENTED TO THE THIRD LENS ELEMENT ADJACENT TO THE DIAPHRAGM, AND THE BACK LENS COMPONENT HAVING FOUR SIMILAR LENS ELEMENTS POSITIONED SO THAT THE LENS SYSTEM IS SYMMETRICAL.

e i United Stan.- T w 0 @T [111 3,865,471 McCrobie r Feb. 11, 1975 [541 LENS SYSTEM FOR Primary Examiner- John K. Corbin PHOTOELECTROPHORETIC COPYING Attorney; Agent, or Firm-James J. Ralabate; David C MACHINE Petre; Charles E. Smith [75] lnventor: George L. McCroble, Upland, Calif.

[73] Assignee: Xerox Corp., Stamford, Conn. I

A symmetrical copying lens system having front and [22] Filed 1974 back compound lens components with a centrally lo- [211 Appl. No.: 430,269 cated diaphragm therebetween adapted to an optical system of a photoelectrophoretic copy machine which can be used at H magnification. The front lens com- 57 ABSTRACT [52] US. Cl. 350/215 ponent has four lens elements including in the follow- Gozb 9/62 ing order, a first lens element of positive power. a secle 0 I u v e I o a v e I I a a a I I e a e I p e a n v I n I n a v e I e II a ment of positive power and a fourth lens element of [56] Rem'ences cued negative power cemented to the third lens element ad- UNITED STATES PATENTS jacent to the diaphragm, and the back lens component 3,524,699 8/1970 Mori 350/215 having four similar lens elements positioned so that the lens system is symmetrical.

1 Claim, 1 Drawing Figure OBJECT PLANE DIAPHRAGM l I l l l LENS SYSTEM FOR PHOTOELECTROPHORETIC COPYING MACHINE BACKGROUND OF THE INVENTION This invention relates to a lens system, and more particularly to a symmetrical lens system which is particularly suited to an optical system used in photoelectrophoretic copy machines.

In the photoelectrophoretic imaging process, wherein light patterns of black and white or full color original information are projected onto a photosensitive member to form a copy of the information on the member, a lens system is required which focuses the light pattern on the member to reproduce sharp, clear images. The characteristics of prior art lens systems for copiers such as the size of field angle that can be tolerated, degree of resolution and other rating factors are to a large extent dependent on the speed, or f-number of the lens system. As a general matter, it is known that as the f-number decreases, the overall performance of the copier lens system declines noticeably if the field angle remains constant. As a result, the lens system used in the present copiers generally maintain fnumbers in the range off (6.3) tof(l 1.0) to assure good resolution at resonable field angles and over a wide spectral range to form images of adequate quality for the copier environment.

With the advent of more demanding copying systems, such as photoelectrophoretic systems, wherein wavelengths of light throught the visible spectrum pass through the lens systems, problems involving chromatic aberration called secondary color and oblique spherical aberration arise with prior art lens systems. For example, with regard to secondary color, in this situation, light rays of different wavelengths in the same ray bundle are displaced a small distance from one another upon reaching the image plane. This displacement causes an obvious depreciation in the image being formed, especially when reproducing color originals if the displacement is allowed to reach proportions discernable by the eye.

The copy lens system disclosed herein maintains high performance characteristics at all field positions throughout -l0 lp/mm. The image field formed by the lens systemhas a large depth of focus which allows easy focusing.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to improve the design of symmetrical type copy lens systems.

It is a further object of the present invention to improve lens systems employed in photoelectrophoretic copy machines.

It is a further object of the present invention to improve the quality of images performed "by copy lens systems over a semi-field angle of approximately 12 and a speed off/3.2.

It is a further object of the present invention to improve the quality of images formed using a light source which has a spectral range from 450 nm to 670 nm.

It is a further object of the present invention to improve the quality of images performed by a symmetrical lens system at 1:1 magnification.

These and other objects of the invention are accomplished by the use of a symmetrical copy lens system which cbmprises front and back lens components witha centrally located diaphragm therebetween adapted to an optical system of a photoelectrophoretic copy machine which can be used at l:l magnification. The lens system forms high quality images at all field positions' throughout 5-10 lp/mm. The image field formed by the lens system is flat and the lens system has a large depth of focus which allows easy focusing.

The front lens component has four lens elements including, in the following order, a first convex-concave lens element of positive power; and a second convexconcave lens element of positive power; a third convexconcave lens element of positive power cemented to a fourth convex-concave lens element of negative poweradjacent to the diaphragm, and the back lens component having four similar lens elements positioned so that the lens system is symmetrical.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS The lens system includes two compound lens com ponents of four lens elements each having a diaphragm located therebetween. The eight lens elements are located so that the entire lens system is symmetrical about the diaphragm.

The front portion of the system includes lens element I which is a positive power lens, lens element II which is a positive power lens, lens element III which is a positive lens and lens element IV which is a negative power lens.

The lens elements inthe back portion of the lens system which include lenses V, VI, VII, and VIII are of the same general configuration as lenses IV, III, II and I respectively, arranged in a complementary manner in the rear portion of the lens system in order to achieve a symmetrical lens system. The FIGURE shows the front portion of the lens system as including lens element l which is a convex-concave lens, lens element II which is shown as a convex-concave lens, lens element III which is shown as a convex-concave lens, and lens element' IV which is shown as a convex-concave lens. The specific sizes, shapes and radii of the individual lens elements are only shown illustratively in the FIGURE and are not necessarily intended to be presented to scale. For instance, lens element I could be a double convex lens as long as its power remains positive. Similar changes can be made in the other lens elements of the system and the same is true of the back portion lens elements.

The parameters of the lens system are based on measurements taken on the system as shown in the FIGURE. The symbol S generally refers to the length of air spaces between elements in the system and the term T refers to the thickness of the lens elements, both distances being measured in inches along the center line of the lens system. Referring to the FIGURE, S1 is the distance between the object plane and lens element 1, S2 is the distance between lens elements I and II, S3 is the distance between lens elements II and Il, S4 is the distance between lens element IV and the diaphragm opening. S is the distance between the diaphragm opening and lens element V, S6 is the distance between lens elements VI and VII, S7 is the distance between lens elements VII and VIII. S8 is the distance between the image plane and lens element VIII and S8 equals 81.

T1 is the thickness of lens element 1, T2 is the the thickness of lens element ll, T3 is the thickness of lens element lll, T4 is the thickness of lens element IV, T5 is the thickness of lens element V, T6 is the thickness of lens element Vl, T7 is the thickness of lens element VII and T8 is the thickness of lens element VII]. in addition, lens element I has radii R1 and R2, lens element tion have been described in detail, other forms which are different in precise detail are possible.

5 What is claimed is: l. A symmetrical type copying lens system having an aperture of substantially f/3.2 magnifying the object format by .l:] magnification, said lens system being corrected for spherical abberation and chromatic abberation including secondary color, lateral and longitudinal chromatism, coma, astigmatism, distortion and field curvature, comprising:

a. a front compound component including lens element 1 of positive power, lens element ll of positive ll has radii R3 and R4, lens element III has radii R5 and P lens element of l- Power, and l R6, lens element W has radii R6 and R7, lens element element IV negetlve Power between the ebleet v has radii R8 and R9, lens element W has radii R9 and plane and dlaphragmi R10, lens element vll has radii R11 and R12, and lens a back compound component Including lens element Vlll has radii R13 d R14, ments V, VI, VII, and VIII the same general config- In the chart below, Radii (R),Thickness (T),Spacing uration as ns I II an 1 sp ti ly, ar- (s) are expressed in inches and the negative sign indianged in a complementary manner 1n the rear por-' cates radii on centers of curvature lying on the object i n f h lens y em In r er to chi e a symside of their vertices. metrical lens system;

In many prior art copires, the correction of seconc. constructional data relating to said lens system dary color is particularly important. When the lens syshaving comprehensive values as given in the chart tem disclosed herein is in this type of color copier at 1:1 hereinbelow wherein S, designates the air space hemagnification at a speed of f/3.2 secondary color eftween the object plane and lens element 1, S desigfects are reduced. The reduction covers wavelengths in nates the air space between lens elements I and ll, the range from 450 to 670 nm when the values shown 8;, designates the air space between lens elements in the Chart set forth hereinbelow are maintained. II and Ill, 8, designates the air space between lens The following chart is an example of cnstructional element IV and the diaphragm opening, 8 desigdata for the preferred embodiment of this invention. In nates the air space between the diaphragm opening the chart, the radii of curvature R, the thickness t, the and lens element V, 8., designates the air space bespacing s, the indices or refraction Nd and the Abbe tween lens elements Vi and VII, 8, designates the numbers V,, are all expressed in the customary manner: air space between lens elements VI] and VIII, 5,, is

CHART E.F.L. 10.5" /3.2

LENS RADll (R) THICKNESS (1) SPAClNGts) Rlg liR c- ABBE INDEX (Nd) Nolvn) s, 14.912 R, 7.244 l r, 0.743 1.69l 54.7

s,= 0.056 R 3.8l2 11 r, =0.570 1.564 60.8

S,= 0.055 R, 4.126 Ill 1,, 0.730 1.699 49.7

R. 24.907 W l, 0.421 1.640 34.6

S, 1.470 s 1.470 R 2.246 v r, 0.421 1.640 34.6

s.,= 0.055 R,, 7.493 vll t 0.570 1.564 60.8

R, 3.8l2 a S 0.056 la 17.860 vlll 1.. m 1.691 54.7

ment VIII,

T is the thickness of lens element I, T is the thick- VIII,

lens element lens element l of Radii R and R lens element lI 9f Radii R and R lens element III of Radii R and R6,

ness of lens element lI, T is the thickness of lens 5 lenselement IV of Radii R and R lens element V element III, T the thickness of lens element IV, of Radii R and R lens element VI of Radii R and T is the thickness of lens element V, T is the R lens element VllofRadii R and R12. lens elethickness of lens element VI, T, is the thickness of ment VIII of Radii R and R E.F.'L. 10.5" [/32 LENS RADII (R) THICKNESS (r) SPACING (s1 REFRAC- ABBE TIVE INDEX (Nd) NO. (V11) s 14.912 R 7.244 1 r, 0.743 1.691 54.7

s 0.055 R 4.126 111 1, 0.730 1.699 49. R. 24.907

s. 1.470 s,,= 1470 R 2.246 v 1, 0.421 1.640 34.6

s.,= 0.055 7.493 R,, v11 1, 0.570 1.564 60.8

S 0056 R l7.860 v111 1,.=0.743

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 8'6 5 3:? Dated February 1]. 197 5 Inventor) George L. McCrobie It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 34, delete "Vi" and insert VI-.

Column 6,

for LENS VIII, under Refractive Index (Nd) which is blank, insert --l.69l--.

Column 6, for LENS VIII,

under Abbe No. (Vd) which is blank, insert --54.7-.

and Trademarks F ORM PO-I 050 (10-69) USCOMM'DC 6S76-PG9 ILS. GOVERNMENT PRINTING OFFICE "ll 0-3I-l8l, 

